A limitation in the research and treatment of Central Nervous System (CNS) or Peripheral Nervous System (PNS) diseases is the conventional recognition that terminally differentiated neurons are significantly limited in their ability to proliferate. Accordingly, any treatment of CNS or PNS diseases that requires transplant of terminally differentiated neurons is difficult to accomplish.
One proposed approach to overcoming this difficulty has been to culture large numbers of mitotic cells exhibiting neuronal progenitor cell characteristics (“CPCs”). Such cells could theoretically differentiate in vivo into neurons that could function in the treatment of CNS and/or PNS diseases. Alternatively, CPCs might be differentiated in vitro into neurons and then transplanted into patients. However, such CPCs are rare and difficult to isolate from donors. Therefore, conventionally, researchers have attempted to obtain CPCs from treated embryonic and fetal stem cells (collectively referred to as “embryonic stem cells” hereinafter).
Embryonic stem cells, which are pluripotent cells, have been used to generate a large variety of tissue types, and could be a source of CPCs. I. Weissman, Stem cells: units of development, units of regeneration, and units in evolution (Review). Cell 100, 157-168 (2000). However, the use of embryonic stem cells raises a number of ethical concerns, and so is a disfavored source of stem cells for production of CPCs. Additionally, embryonic stem cells can be tumorigenic, which generates safety concerns as to any transplant procedure that could potentially result in the delivery of embryonic stem cells to a patient such as creation of a CPC graft from embryonic stem cells.
Some researchers have attempted to utilize other types of stem cells, such as mesenchymal stem cells in the production of CPCs. U.S. Patent Application 20030003090 of Prockop, et al., filed Jan. 2, 2003 , and entitled “Directed in vitro differentiation of marrow stromal cells into neural cell progenitors” discloses that the expression levels of both NSE and vimentin were increased in human mesenchymal stem cells after their incubation with 0.5 millimolar IBMX and 1 millimolar dbcAMP. The increase in NSE and vimentin mRNAs coincided with the appearance of neural cells in the cultures. However, Prockop et al. reported that there was no change in the expression level of either MAP1 B or TuJ-1. Since NSE, MAP1 B, and TuJ-1 are early neuron-characteristic markers, and vimentin is an early marker for glia, Prockop et al. suggested that the hMSCs transdifferentiated in vitro into some early progenitors of either neurons or glia. However, the early progenitor cells of Prockop may be undesirable for use because they seem to display a very immature neuronal phenotype whose clinical efficacy is not well understood.
Accordingly, there is a scarcity of conventionally available and suitable sources of CPCs for use, for example, in the research and treatment of CNS or PNS diseases. Further, there is a scarcity of methods that can be used to produce such CPCs in a suitable manner suitable for use. What are needed are methods and compositions that overcome such problems.